Invasive Species, Agitating Agriculture?

Well that management section was fun, I can barely remember what it's like to write about anything else. But the past is the past, I need to knuckle down and rattle through some more invasive species related capers. So, onwards we go!

When I was chatting with Hugo Watkins the other day about his farming blog, I flippantly asked him if he'd done a piece on the impact of invasive species on agriculture yet. That very second, the cogs in my brain slowly clicked into action.

An actual X-ray of the inside of my skull.

*Wait, I've just suggested something invasive species related...that means... Gah I know the answer to this one..*

...15 minutes later...

*That means I can write about it!*

And write about it I shall! Because it turns out, the impact of invaders on agriculture has been quite a big deal. AND it's likely to increase in future.

So, whereas Hugo's blog discusses how agriculture is contributing to environmental change, I'm looking at how environmental change is contributing to agriculture. Neat, huh?

Invasive species and agriculture, how costly could the impacts be?

Earth is now home to over 7 billion hungry humans, and we're heavily reliant on agriculture for food. However, invasive species can cause agricultural product losses worth more than a trillion US dollars per year (Oerke and Dehne, 2004). According to Ziska et al (2011), in their 'agronomics'  paper, ¹/₄ of U.S.A's gross agricultural product is lost to invasive species each year. Yipes.

For example. Asian soybean rust (Phakopsora pachyrzi), an invasive pathogen, has potential to inflict major soybean production damage in the U.S.. It is thought to have arrived from South America in 2004, having been carried by Hurricane Ivan. In future, with storminess expected to increase under climate change, its spread and negative agriculture effects could become worse (Ziska et al., 2011).

U.S states with confirmed detections of Asian soybean rust in 2006. Source: Economic Research Service

Invasive weeds can also pose agricultural problems. For example, Follak and Essl (2013) have documented the spread and agricultural impact of Sorghum halepense, an emerging invasive species in Central Europe.

The Central Asian native first arrived in Austria in 1871, was rare until 1970, but has expanded rapidly since 1990 and even more so since the new millennium. The S. halepense invasion puts approximately 41% of maize fields and 40% of oil pumpkin fields at risk of yield losses.

Cumulative records of S. halepense in Austria. Source: Follak and Essl (2013)

S. halepense can also act as a reservoir for Maize Dwarf Mosaic Virus (MDMV). Evidence for this comes from N. Italy, where S. halepense is widesprad and MDMV is commonly found on maize plants (Ivanovic et al., 1995), and Hungary, where yield losses from maize fields were reported to be up to 30.5% (Peti, 1983 cited in Ziska et al., 2011). 

Sorghum halepense, reducing Austrian agricultural yields since 1871.

The fast and ongoing spread of S. halepense is likely to increase under climate warming as more habitat becomes suitable.  In fact, all major agricultural areas in Austria and Germany expected to be climatically suitable by 2050 (Kleinbauer et al., 2010).

Additionally, management is troublesome, given that it has high seed production, high regeneration potential and is only sensitive to specific, high cost herbicides (Follak and Essl, 2013). Double yipes.

Invasive insects can also initiate farming frustrations. For example, African honey bees are moving north through America. These invaders readily capture feral and managed European honey bee colonies, with subsequent impacts on fruit production. Once again, this spread is likely to be facilitated further by climate warming (Ziska et al., 2011).

Current and projected range of Africanised honey bees. Black areas are where it is currently present. Grey areas represent the area that could support the bee if there are 120 days where the max temperature is >10°C

An even more serious insect invasion took place at the start of the 20th century when the introduction of the boll weevil (Anthonomus grandis) to the U.S. from Mexico resulted in almost the complete eradication of cotton crops in the U.S., with billions of dollars of crop damage (Ziska et al., 2011).

The risk to agriculture from invasive species is only likely to increase in future, not just due to rising temperatures, but also potentially from heightened winds and CO₂ increases. These factors could also interact. For example, the invasive weed, Kudzu, is known to respond strongly to CO₂ increases (Forseth and Innis, 2004) and is likely to move north as temperatures increase (Sasek and Strain, 1990).

Increasing CO₂ concentrations have been shown to increase the biomass of invasive kudzu.

The impacts of this on agriculture will be heightened by the fact that Kudzu can act as a host for Asian soybean rust, which I described above. Treble yipes.

This post has been a bit of a downer so far, so I should probably try and lighten the mood. Our food supply isn't completely doomed. We must also recognise the response of agroecosystems themselves to climate change. For example, rising CO2 could be used by breeders to improve existing cultivars. This could enable them to become more competitive against potential invaders and reduce productivity losses (Ziska et al., 2011).

To conclude, invasive species have been agitating agriculture for quite some time, and look likely to be an even greater annoyance as we move into the future. We should be aware of the impact invasive species can have on important ecosystem services, such as agriculture, and do our utmost to ensure that the future impacts of invaders are not as damaging as it looks like they could be.

Over and out

The Invader Inspector